Signal-to-noise analysis in a counter-pumped fiber Raman amplifier

The light gain efficiency due to Raman scattering in a distributed fiber Raman amplifier is a subject of our investigation. The detailed analysis of noise properties at one-wave optical signal amplification in a single-mode fiber in the scheme of counter-pumped fiber Raman amplifier is realized in the paper. Experimental results of the amplified spontaneous emission with backward pumping as a base of optical noise evaluation are presented. Raman gain spectrum for a coherent Stokes low-powered signal is calculated and it is compared with the observed spectrum of non-coherent amplified spontaneous emission noise. It is shown that an output optical signal has higher gain than the amplified spontaneous emission and it results in the appreciable growth in the output optical signal-to-noise ratio.